THIS STUDY aims at evaluating the relationship between the state of cerebral collateral blood vessels and the functional outcome of patients with acute ischemic stroke with or without thrombolytic therapy. The study was carried out in the inpatient sector of the neurology department at Ain Shams University hospitals. A sample of 30 patients with acute ischemic stroke was collected and CT cerebral angiography was done to assess the clot burden score and the collateral score. MRI stroke protocol was performed to assess the structural collaterals through diffusion weighted image, FLAIR, NIH, and MRS. There was a statistical significant difference between stroke patients who received treatment and patients who did not receive traetment in relation to collateral score, clotting burden score, modified Rankin scale after three months, onset by hours and door to needle. Computed tomography angiography and MRA played an important role in the assessment of the collateral blood vessels, clot burden score, infract volume and also predicted the need for recombinant tissue plasminogen activator (rtPA) and the degree of improvement. There was a significant correlation between the modified Rankin scale and the clotting burden scale, the collateral scale and the infract volume. Patients with good NIH score and MRS show a higher level of improvement. It could be concluded that the collateral status as assessed by CTA is considered an excellent predictor of a favorable functional outcome in acute ischemic stroke patients. Patients with good collateral status will benefit from recanalization and patients with poor collaterals likely will not benefit even when recanalization occurs.